For oil recovery a well is drilled and a well tubular such as a casing or a liner is introduced into the well. The outside diameter of the well tubular is smaller than the inside diameter of the wellbore, thereby forming an annular space between the wall tubular and the wellbore. The well tubular is perforated at one or more zones in order to facilitate the flow of hydrocarbons into the tubular and subsequent flow upstream for recovery. Occasionally contaminating materials such as water and sand are produced along with the hydrocarbons from a part of the subterranean formations surrounding the well tubular. In these situations it is desirable to seal off the well tubular from one or more parts of the annular space. Also in other situation it may be desirable to seal off the annular space.
To seal off a desired part of, e.g., a well one possibility is to isolate the internal part of the well tubular using temporary packers. Cement or another hardenable composition is then pumped down to the isolated zone to seal the perforated openings in the desired part of the well tubular. If production is subsequently desired from a zone situated further downstream in the casing, removal or penetration of the seal is required.
In the past the placing of a “treatment fluid”, e.g. an acid, a polymer, or cement, within a wellbore has been accomplished by use of a “bailer” which is introduced into the well on a wireline or the like. The bailer contains a specific volume and is activatable due to density differential of the treatment fluid relative to the natural fluids present in the wellbore at the time and location of treatment. Even modified bailer systems do not satisfactorily deliver a predetermined amount of a treatment fluid at the exact location, especially in highly deviated wells or in the well tubular which has become “cork-screwed”. Thus, a number of other systems have been devised for deploying a “treatment fluid” at a proper location for e.g. providing a seal.
U.S. Pat. No. 6,955,216 discloses a device for injecting a fluid into an earth formation surrounding a well. The device comprises a body suitable for being arranged in a well bore and provided with a fluid chamber for storage of suitable sealant and a pair of inflatable packers arranged to isolate a portion of the well bore between the packers upon inflating the packers. The suitable sealant in then injected under pressure into the formation through perforations isolated between the packers. The sealant composition is disclosed to be a suitable material, such as a vulcanised or unvulcanised rubber composition.
U.S. Pat. No. 4,972,906 discloses the use of a mixture of a liquid epoxy material and a hardener for plugging a zone in a subterranean zone. The epoxy material used is heavier than the fluid in the well, and it is further characterized as being free of solids and having a low viscosity at downhole temperature and pressure. The material is placed in a well by the use of a positive displacement bailer. Hence, the liquid epoxy material exhibit an undesirable axial dispersion which may only partially be overcome by using an excessive amount of the epoxy material. Thus, the method has the drawback of not facilitating a site-specific placing of the seal.
Thus, there is a need to devise improved procedures for introducing a seal in an annular space between a well tubular and the surrounding formation.